Speaker suggestions for less than ideal accoustics

Apart from the windows and the tile floor, which may give you reflections and some harshness in the treble, the fire place, loft and large room size probably make this a great room for listening (lots of space and uncorrelated reflections). If you place speakers with back to windows and get a rug then you may not even need to worry about treble reflections

My guess is that the speakers that give you the best lower base response and that are least harsh sounding in upper mid and treble might work for you. You have a large room to fill, perhaps the Def Techs with that big 10" woofer might give you the umph you will need.... provided you are comfortable the "airy" highs these speakers are known for.

good luck!

To follow up on Cdc's comments

I use ATC SCM 100 active monitors, an SCM 0.1/15 sub and the SCM 20's. I fear the 20's may be a little small for your needs (they definitely need a sub). I am not sure about the 50's as I have not heard them.

What I can confirm, as Cdc says, the 100's are indeed quite comfortable playing louder than anything I have ever heard outside of a rock concert. And with very low levels of distortion or compression.

As a pro speaker primarily used for mixing/mastering they have good dispersion of the sound field with a very even energy level throughout a large room...practically speaking this means that speaker placement is not critical (there is a solid image but no critical sweetspot). They also play consistently at all sound levels. These two factors may make them highly suitable for your application.

However....

A caveat here, these really are "studio monitors" primarily used by professionals for critical listening. You will get ruthlessly accurate sound and a dynamic range that only pros demand and wives/neighbours may hate. Everything is critically damped in the design. The nice sounding harmonic colourations and warm resonant base commonly found in most widely appealing speakers, are totally absent.

They are also, admittedly, not pretty => see the pictures I have posted of my system.

The word "monitor" has been freely adopted by almost all consumer speaker manufacturers and has become quite meaningless, however, in this particular case, "Studio Control Monitor" really does mean something. The large ATC SCM 100 model remains principally designed for and sold to professionals and will probably never be very popular with consumers.